1. Field of the Invention
The present invention relates to an electromagnetic relay and more particularly to the electromagnetic relay to be used as a vehicle-mounted electromagnetic relay or a like.
The present application claims priority of Japanese Patent Application No. 2005-114584 filed on Apr. 12, 2005, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, an electromagnetic relay is used for electrical components of automobiles or a like. The general and conventional electromagnetic relay being used as a vehicle-mounted one is described below.
FIG. 1 is a perspective view showing configurations of a conventional electromagnetic relay 10. FIG. 2 is partially exploded perspective view showing configurations of the conventional electromagnetic relay 10 of FIG. 1. FIG. 3 is a partial side view showing configurations of the conventional electromagnetic relay 10 of FIG. 1. As shown in FIG. 1, on a base 7 is mounted a coil 1 on which a movable contact 3a is placed with a yoke 2 and an armature 4 being interposed between the coil 1 and movable contact 3a. As shown in FIG. 2, the electromagnetic relay 10 operates in a manner in which an end of its movable contact spring 3 serves as the movable contact 3a which alternately comes in contact with a normally closed fixed contact 5a of a normally closed fixed contact member 5 placed so as to face the movable contact 3a and a normally open fixed contact 6a of a normally open fixed contact member 6 also placed so as to face the movable contact 3a. 
Moreover, the movable contact spring 3 is in contact with the armature 4 with a spool 8 and an iron core 9 being interposed between the movable contact spring 3 and the armature 4.
In FIGS. 1 to 3, when a voltage is applied to the coil 1, the movable contact spring 3 and the movable contact 3a move toward a direction A (FIG. 3) and, when striking the normally open fixed contact 6a to come into physical contact on surfaces of the movable contact 3a and the normally open fixed contact 6a, the movable contact spring 3 bends with attractive magnetic forces and the movable contact 3a slides on the normally open fixed contact 6a toward a direction B (FIG. 3).
FIGS. 8A and 8B are partial side views explaining operations of the movable contact 3a, normally closed fixed contact 5a, and normally open fixed contact 6a when viewed from a direction to which the contact slides (same as the direction B in FIG. 3) in the conventional electromagnetic relay 10. FIG. 8A shows operations in a non-excited state and FIG. 8B shows operations in an excited state. As shown in FIG. 8A, in the conventional electromagnetic relay 10, when a voltage is applied to its coil 1 shown in FIGS. 1 and 2, the movable contact 3a strikes the normally open fixed contact 6a and slides thereon. An angle which a surface of the movable contact 3a being opposed to the normally open fixed contact 6a, when viewed from the direction to which the movable contact 3a slides on the normally open fixed contact 6a, forms with a surface of the normally open fixed contact 6a being opposed to the surface of the movable contact 3a when viewed from the sliding direction is set to be fixed so that the movable contact 3a is parallel to the normally open fixed contact 6a. As shown in FIG. 8B, when an voltage is applied to the coil 1 (as shown in FIGS. 1 and 2), the movable contact 3a comes into collision with the normally open fixed contact 6a and the movable contact 3a is moved by repulsion in a manner to become a movable contact 11 shown by dashed lines which is the movable contact 3a resulting from the movement. This movement is called a “contact bounce”.
Generally, a very large amount of current flows through loads such as a lamp or a capacitor when a contact is closed. Therefore, the above-described contact bounce occurring at the time of closing the contact has much effect on a contact life of the electromagnetic relay 10.
If a contact bounce occurs in a state where a large amount of current is flowing, arc currents are produced and there is a danger of an occurrence of a failure such as welding of a contact or locking caused by a protrusion or hole formed on a contact surface.
In order to decrease the occurrence of the bounce at time of closing the contact, by making stiffness of the fixed contact member lower and by making the fixed contact member itself elastic, repulsion is suppressed at a time of collision of the movable contact, which enables the occurrence of the bounce to be reduced. This technology is disclosed in Patent Reference I (Japanese Utility Model Application Laid-open No. Hei05-83994).
As described above, in the Patent Reference 1, for example, in order to decrease the occurrence of arc currents, an electromagnetic relay is so configured that a fixed contact spring itself is made to have elasticity, however, to make the fixed contact member itself have elasticity, it is necessary to make a plate thickness be small, which causes a decrease in current-carrying capability due to reduction in a cross-sectional area for current carrying. Moreover, if a vibration-isolating material is to be mounted thereon, new problems of an increase in component counts accompanied by an increase in the number of man-hours or in costs arise.